Overview of the STL & Assorted C++ features

1. Junaed Sattar November 19, 2008 Lecture 12 Overview of the STL &Assorted C++ features

2. The STL • Stands for Standard Template Library • set of C++ template classes to provide common programming data structures and functions • officially (from SGI's STL site): • library of container classes, algorithms, and iterators • provides many of the basic algorithms and data structures of computer science

3. Basic Characteristics of the STL • a generic library, meaning that its components are heavily parameterized: • almost every component in the STL is a template. • make sure that you understand how templates work in C++ before you use the STL!

4. Categories • Categorized in the following groupings • Containers and algorithms • classes for containing (holding) other objects and related algorithms for data manipulations • Iterators • generalization of pointers, which applies to any object stored in container classes • Concepts, Modeling, Refinement • rules about the set of types that may correctly be substituted for the formal template parameters • Utilities • Miscellaneous utilities

5. Containers/Algorithms • Includes classes vector, list, deque, set, multiset, map, multimap, hash_set, hash_multiset, hash_map, and hash_multimap • Each of these classes is a template, and can be instantiated to contain any type of object • Generic algorithms manipulate data stored in these container objects

6. Container: Vector • Avoids managing dynamic memory by hand vector<string> SS;SS.push_back("The number is 10");SS.push_back("The number is 20");SS.push_back("The number is 30");// Loop by indexfor( int ii=0; ii < SS.size(); ii++ ) { cout << SS[ii] << endl; }

7. Algorithm Example • // Reverse the elements in the Vector • reverse(v.begin(), v.end()); • // Loop by index • for( int ii=0; ii < SS.size(); ii++ ) { • cout << SS[ii] << endl; • } • Outputs: • The number is 30 • The number is 20 • The number is 10

8. Iterators • STL class to represent position in an STL container • i.e. objects that point to other objects • An iterator is declared to be associated with a single container class type • i.e. to access a vector of strings, we require an iterator to vector<string>

9. Types • input_iterator: Read values with forward movement. • output_iterator: Write values with forward movement. • forward_iterator : Read or write values with forward movement. These combine the functionality of input and output iterators with the ability to store the iterators value. • bidirectional_iterator: Read and write values with forward and backward movement. • random_iterator: Read and write values with random access. These are the most powerful iterators, combining the functionality of bidirectional iterators with the ability to do pointer arithmetic and pointer comparisons. • reverse_iterator: Either a random iterator or a bidirectional iterator that moves in reverse direction.

10. Iterators: Vector • vector<string> SS;SS.push_back("The number is 10");SS.push_back("The number is 20");SS.push_back("The number is 30");vector<string>::iterator cii; • for(cii=SS.begin(); cii!=SS.end(); cii++){ cout << *cii << endl;}

11. Another example • #include <iostream.h>#include <vector.h>#include <algo.h>#include <iterator.h> • int main (int argc, char *argv[]){ int n = atoi (argv[1]); vector<int> v;for( int i = 0; i < n; i++ ) v.push_back (i); • random_shuffle (v.begin(), v.end()); • // print • copy( v.begin(), v.end(), ostream_iterator<int>( cout, "\n")); • }

12. Sort: STL Style • void sort( iterator start, iterator end ); • void sort( iterator start, iterator end, StrictWeakOrdering cmp ); • sorts the elements in the range [start,end) into ascending order • if strict weak ordering function object cmp is given, then it will be used to compare two objects instead of the < operator.

13. Example sort • vector<int> v; • sort( v.begin(), v.end() ); • And also, • int array[] = { 23, -1, 9999, 0, 4 }; • unsigned int array_size = 5; • sort( array, array+array_size );

14. Compare function • bool cmp( int a, int b ) { return a > b;} • sort( v.begin(), v.end(), cmp );

15. Auto pointers • Pointers, but do not require explicit deallocation • i.e. does not have to be “delete”-ed • but only individual pointers, not arrays • again, this is a templated type • similar to garbage collection in Java

16. Auto Pointer Example • #include <iostream>#include <memory>using namespace std;class X { public: X() { cout << "constructing\n"; } ~X() { cout << "destructing\n"; } void f() { cout << "Inside f()\n"; }}; • int main() {auto_ptr<X> p1(new X), p2;p2 = p1; // transfer ownershipp2->f();X *ptr = p2.get(); // can assign to a normal pointerptr->f();return 0;}

17. More STL Reference • The STL Book (it's in the course outline) • STL Homepage: http://www.sgi.com/tech/stl/ • Another tutorial on the STL • http://www.cs.brown.edu/people/jak/proglang/cpp/stltut/

18. Namespaces • allows grouping of entities (classes, functions, variables etc) under one name • similar to a Java package • helps to create sub-scopes for identifiers • To declare a namespace: namespace namespace_identifier {// declare entities here}

19. Example usage namespace Probability { double pdf, cdf; double *distribution; class GaussianDistribution { ... }; } int main() { using Probability::GaussianDistribution; GaussianDistribution GD; ... }

20. The using keyword • used to introduce a name from a namespace into the current declarative region • i.e. using Probability::pdf • also can be used to introduce entire namespaces • using namespace Probability

21. utility of namespaces • functionality of namespaces is especially useful to avoid redefinition errors • also known as naming collision • in the case that a global object or function uses the same identifier as another one • commonplace in large projects, multiple programmers working on the same program

22. “Collision avoidance” namespace Cars { double velocity = 10; }; namespace Planes { double velocity = 1000; } int main(){ cout << Cars::velocity << “\n”; cout << Planes::velocity << “\n”; }

23. Namespace using scope • using, using namespaceare valid in the declaring code block, or global scope if declared at the beginning of the program • remember, curly braces create code blocks In C++

24. C++ Exceptions • react to unexpected circumstances in code • using exception handlers • place suspect code under inspection • using a try block • control goes to exception handlers in case of exception • all the catch blocks

25. Syntax • try{ // place your code here, for example: ch = new char[100]; throw 100;}catch( std::bad_alloc ex ){ cout << ex.what();}catch( int exi ) { cout << exi; }catch(...){ // catches everything else, default hander}

26. Exception Throwing • thrown exception can be of any type • basic types (int, char, float... ) • any object derived from the standard class called exception • exception is declared in the header <exceptions> • virtual member function what returns a null-terminated character sequence (char *) • override in derived classes to contain some sort of description of the exception

27. User-defined exceptions • functions throwing exceptions: • void GetRoots() throw (int) • throws an integer exception (catch int) • void GetRoots() • can throw any type of exception • void GetRoots throw () • cannot throw any type of exception

28. Custom Exception Class class CustomException: public exception { virtual const char* what() const throw() { return "Custom exception happened"; } }; int main() { try { CustomExcpetion custEx; throw custEx; } catch( exception& e ){ // reference to base is ok cout << e.what() << endl; } return 0; }

29. Standard Library Exceptions

30. Miscellaneous • C++ structs: • Same as classes, except by default, everything is public (classes have everything private by default) • C structs do not have methods. Only data. • C has no concept of data-function binding • struct Complex { private: double real, imaginary; public: Complex(); ...}

31. return(EXIT_SUCCESS)? • Concluding remarks.